Fix incorrect data type choices in some read and write calls.

Recently-introduced code in reconstruct.c was using "unsigned"
to store the result of read(), pg_pread(), or write().  This is
completely bogus: it breaks subsequent tests for the result being
negative, as we're being reminded of by a chorus of buildfarm
warnings.  Switch to "int" as was doubtless intended.  (There are
several other uses of "unsigned" in this file that also look poorly
chosen to me, but for now I'm just trying to clean up the buildfarm.)

A larger problem is that "int" is not necessarily wide enough to hold
the result: per POSIX, all these functions return ssize_t.  In places
where the requested read or write length clearly fits in int, that's
academic.  It may be academic anyway as long as we constrain
individual data files to 1GB, since even a readv or writev-like
operation would then not be responsible for transferring more than
1GB.  Nonetheless it seems like trouble waiting to happen, so I made
a pass over readv and writev calls and fixed the result variables
where that seemed appropriate.  We might want to think about changing
some of the fd.c functions to return ssize_t too, for future-proofing;
but I didn't tackle that here.

Discussion: https://postgr.es/m/1672202.1703441340@sss.pgh.pa.us

Author: tglsfdc

src/backend/access/transam/xlog.c

@@ -2280,7 +2280,7 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 			char	   *from;
 			Size		nbytes;
 			Size		nleft;
-			int			written;
+			ssize_t		written;
 			instr_time	start;
 
 			/* OK to write the page(s) */

src/backend/backup/basebackup.c

@@ -117,8 +117,8 @@ static void perform_base_backup(basebackup_options *opt, bbsink *sink,
 								IncrementalBackupInfo *ib);
 static void parse_basebackup_options(List *options, basebackup_options *opt);
 static int	compareWalFileNames(const ListCell *a, const ListCell *b);
-static int	basebackup_read_file(int fd, char *buf, size_t nbytes, off_t offset,
-								 const char *filename, bool partial_read_ok);
+static ssize_t basebackup_read_file(int fd, char *buf, size_t nbytes, off_t offset,
+									const char *filename, bool partial_read_ok);
 
 /* Was the backup currently in-progress initiated in recovery mode? */
 static bool backup_started_in_recovery = false;
@@ -525,7 +525,7 @@ perform_base_backup(basebackup_options *opt, bbsink *sink,
 		{
 			char	   *walFileName = (char *) lfirst(lc);
 			int			fd;
-			size_t		cnt;
+			ssize_t		cnt;
 			pgoff_t		len = 0;
 
 			snprintf(pathbuf, MAXPGPATH, XLOGDIR "/%s", walFileName);
@@ -2079,11 +2079,11 @@ convert_link_to_directory(const char *pathbuf, struct stat *statbuf)
  *
  * Returns the number of bytes read.
  */
-static int
+static ssize_t
 basebackup_read_file(int fd, char *buf, size_t nbytes, off_t offset,
 					 const char *filename, bool partial_read_ok)
 {
-	int			rc;
+	ssize_t		rc;
 
 	pgstat_report_wait_start(WAIT_EVENT_BASEBACKUP_READ);
 	rc = pg_pread(fd, buf, nbytes, offset);
@@ -2096,7 +2096,7 @@ basebackup_read_file(int fd, char *buf, size_t nbytes, off_t offset,
 	if (!partial_read_ok && rc > 0 && rc != nbytes)
 		ereport(ERROR,
 				(errcode_for_file_access(),
-				 errmsg("could not read file \"%s\": read %d of %zu",
+				 errmsg("could not read file \"%s\": read %zd of %zu",
 						filename, rc, nbytes)));
 
 	return rc;

src/bin/pg_combinebackup/reconstruct.c

@@ -504,15 +504,15 @@ make_rfile(char *filename, bool missing_ok)
 static void
 read_bytes(rfile *rf, void *buffer, unsigned length)
 {
-	unsigned	rb = read(rf->fd, buffer, length);
+	int			rb = read(rf->fd, buffer, length);
 
 	if (rb != length)
 	{
 		if (rb < 0)
 			pg_fatal("could not read file \"%s\": %m", rf->filename);
 		else
 			pg_fatal("could not read file \"%s\": read only %d of %d bytes",
-					 rf->filename, (int) rb, length);
+					 rf->filename, rb, length);
 	}
 }
 
@@ -614,7 +614,7 @@ write_reconstructed_file(char *input_filename,
 	{
 		uint8		buffer[BLCKSZ];
 		rfile	   *s = sourcemap[i];
-		unsigned	wb;
+		int			wb;
 
 		/* Update accounting information. */
 		if (s == NULL)
@@ -641,7 +641,7 @@ write_reconstructed_file(char *input_filename,
 		}
 		else
 		{
-			unsigned	rb;
+			int			rb;
 
 			/* Read the block from the correct source, except if dry-run. */
 			rb = pg_pread(s->fd, buffer, BLCKSZ, offsetmap[i]);
@@ -650,9 +650,9 @@ write_reconstructed_file(char *input_filename,
 				if (rb < 0)
 					pg_fatal("could not read file \"%s\": %m", s->filename);
 				else
-					pg_fatal("could not read file \"%s\": read only %d of %d bytes at offset %u",
-							 s->filename, (int) rb, BLCKSZ,
-							 (unsigned) offsetmap[i]);
+					pg_fatal("could not read file \"%s\": read only %d of %d bytes at offset %llu",
+							 s->filename, rb, BLCKSZ,
+							 (unsigned long long) offsetmap[i]);
 			}
 		}
 
@@ -663,7 +663,7 @@ write_reconstructed_file(char *input_filename,
 				pg_fatal("could not write file \"%s\": %m", output_filename);
 			else
 				pg_fatal("could not write file \"%s\": wrote only %d of %d bytes",
-						 output_filename, (int) wb, BLCKSZ);
+						 output_filename, wb, BLCKSZ);
 		}
 
 		/* Update the checksum computation. */